Lyme disease is a multisystem illness caused by infection with the spirochete Borrelia burgdorferi and it is the leading vector-borne disease in the United States. Our current work addresses the following areas in Lyme disease: development of new tests and biomarkers for infection, investigation of persistence of infection with B. burgdorferi in humans, search for the cause of Southern Tick-associated Rash Illness (STARI), and investigation of the role of immune response in Lyme disease and PLDS. One of the main problems in Lyme diagnosis has been the lack of highly specific and sensitive assays for B. burgdorferi and the lack of a test that could be used to assess response to therapy. Such assays should greatly facilitate the accurate diagnosis of Lyme disease and assessment of response to therapy in individual patients. Currently, no such test is available. We have developed a new test using the luciferase immunoprecipitation systems (LIPSs) for profiling of the antibody responses to a panel of B. burgdorferi proteins for the diagnosis of Lyme disease. A synthetic protein consisting of a repeated antigenic peptide sequence, named VOVO, had the best diagnostic performance, similar to the C6 test (a diagnostic test using a peptide ELISA that we have helped develop and is highly sensitive and specific). The VOVO LIPS test displays a wide dynamic range of antibody detection spanning over 10,000-fold without the need for serum dilution;and offers an efficient quantitative approach for evaluation of the antibody responses in patients with Lyme disease. Recent studies have shown that the B. burgdorferi may persist in animals after antibiotic therapy and can be detected by using the natural tick vector (Ixodes scapularis) to acquire the organism through feeding. Whether this occurs in humans is unknown. We have implemented a new clinical protocol to investigate the utility of this approach for identifying persistence of B. burgdorferi in treated human Lyme disease. STARI is a rash similar to the rash of Lyme disease that occurs in persons residing in southeastern and south-central states and is associated with the bite of the lone star tick, Amblyomma americanum. The cause of the rash is unknown, as it is the natural course of the disease. We have a clinical protocol to investigate the cause of the STARI, and we are applying new genomic tools that identify bacteria based on species-specific sequences in the 16S rRNA ribosomal genes to the skin biopsies from patients with STARI. Inflammatory innate immune responses are critical in the control of early disseminated infection, while adaptive immune responses are vitally important, particularly the humoral immune response, in controlling spirochete levels in tissues and resolution of Lyme arthritis in animal models. We are examining the antibody response to immunogenically dominant antigens of B. burgdorferi in PLDS patients and controls. Further investigation of the anti-borrelia immune response may help in elucidating the pathogenic mechanism of PLDS and yield important information for future approaches to diagnosis and treatment. We have a clinical protocol where we use DNA microarrays to characterize gene expression patterns in skin biopsies from individuals with EM, with the aim of capturing the human host response to the pathogen exposure. We are also investigating the differences in immunological response between predominantly lymphocytic meningitis and predominantly neutrophilic meningitis. Results from these studies will serve as a window into the fundamental biology of the infection. We have also shown that the number of natural killer cells, as defined by the CD57 marker or by or CD16+ or CD56+ CD3&#8722;cells is not significantly different between individuals with post-Lyme disease syndrome, individuals who recovered from Lyme disease, and healthy volunteers. We have collaborated in the description of a patient with relapsing fever after exposure in the mountains near Los Angeles, California, USA. Investigations at the exposure site showed the presence of O. hermsi ticks infected with Borrelia hermsii and the presence of rodents that were seropositive for the spirochete, showing that this tick-borne disease is endemic to the San Gabriel Mountains near the greater Los Angeles metropolitan area.